The present invention relates to a method for processing manganese nodules and, more particularly, relates to a method for selective recovery of nickel, copper, cobalt and zinc values contained therein, by predominantly hydrometallurgical means.
Ocean floor nodules containing significant quantities of metal have been viewed as a source for a number of the metals contained therein. The nodules generally contain manganese, iron, copper, nickel, cobalt, zinc, molybdenum, aluminum, magnesium, alkali, and other components, such as clay minerals. Manganese can be present in the nodules generally in an amount of from 10 to 40 weight percent and the nodules have come to be referred to as manganese nodules. Of the many ingredients in the nodules, nickel, copper and cobalt recovery have received major attention as providing an economical source of these metals. In addition, zinc and molybdenum recovery have received attention as providing an economical source of these metals. The nodules generally have not been considered as an economical source of the other metals, and methods have been devised to separate the nickel, copper, cobalt, zinc, and molybdenum from the other components of the nodules.
Since manganese nodules differ considerably in their mineralogical structure and chemical composition from all previously smelted ores, it is not possible to refer to a known ore smelting process for the metallurgical processing of such nodules. Preconcentration of the values by physical processing methods is impossible according to present experience i.e., the manganese nodules must be smelted without being enriched.
Several processes for recovering the values contained in manganese nodules are known. Beck and Messner, in Copper Metallurgy, 1970, pages 70 to 82, examine melting of manganese nodules in an electric arc furnace under reducing conditions with simultaneous slag formation of the manganese. The disadvantage in this process is that an alloy is formed which consists of iron, cobalt, nickel and copper and this alloy is difficult to separate into its individual components.
In other known processes, the manganese nodules are decomposed by sulfate forming roasting or chlorination with gaseous chlorine and/or hydrogen chloride and are then dissolved by leaching with water or diluted sulfuric acid. See, for example, U.S. Bureau of Mines, Rept. Invest. 7473, and German Offenlegungsschrift No. 2,126,175 and the substantially corresponding British Pat. No. 1,347,715. These processes have the disadvantage that the less valuable manganese is also dissolved and must thus be recovered which, in the end, involves undesirably high process costs and technically complicated process stages.
It has also been proposed to selectively reduce the copper, nickel and cobalt contained in the manganese nodules in a first process stage with reduction gas, oil or carbon and to subsequently treat the reduction products in the presence of air with an aqueous ammoniacal-ammonium salt solution thus forming water soluble amine complexes of copper, nickel and cobalt. See, for example, German Offenlegungsschrift Nos. 2,135,733, 2,135,734 and 2,247,497, and the substantially corresponding U.S. Pat. Nos. 3,753,686, 3,734,715 and 3,788,841, respectively. In U.S. Pat. No. 3,728,105, there is disclosed a process in which the manganese nodules are subjected directly to an ammoniacal pressure leaching at 300.degree. C. These processes which operate with ammonia have the disadvantage that complicated process stages are required to circulate the ammonia and to obtain high yields in values.
According to a proposal made in German Offenlegungsschrift No. 2,135,732, and the substantially corresponding U.S. Pat. No. 3,723,095, the manganese nodules are treated at temperatures up to 60.degree. C with an ammoniacal manganese (II) sulfate solution whereby the values which form water soluble amine complexes are separated from the iron and manganese compounds. The drawback of this process is that it is necessary to continuously produce new manganese (II) sulfate and introduce it into the process.